In order to quickly diagnose and repair the relief valve in the hydraulic system,this paper focuses on the structure and principle of several common relief valves,and the relief valve test system is successfully built on the basis of the research.The test system can test different types of relief valves,in the test process,by adjusting the pressure adjustment element of the relief valve,the test system can record various data and the change trend of the data,and judge the performance status of the relief valve.The construction of the test system can improve the accuracy of the fault diagnosis of the relief valve and provide guarantee for the reliable operation of the hydraulic system.At the same time,this paper gives successful cases of diagnosis by using this system.